A known method of manufacturing a multilayer chip inductor as one type of multilayer ceramic electronic component, such as a multilayer chip inductor, is described below.
First, ceramic slurry prepared by mixing magnetic ceramic powder with binder and solvent is coated onto a base film composed PET or the like using a doctor blade to thereby form a green sheet of about tens of microns thick. Next, the green sheet on the base film is cut to a predetermined size and the cut green sheet is peeled from the base film. Then, a multiplicity of through holes are formed to the peeled green sheet in a predetermined disposition. Subsequently, conductor paste prepared by mixing metal powder, binder and solvent is printed to the peeled green sheet using a screen printer and a conductor pattern for a coil is formed to overlap the every through hole with the end of pattern. Next, the green sheets each having the conductor pattern formed thereon are stacked together with dummy sheets in a predetermined order and pressed into one body. Then, the thus obtained pressed member is cut to dimensions corresponding to respective components and the multilayer chips having been cut are fired. Subsequently, conductor paste serving as external electrodes is coated to the predetermined positions of the multilayer chip having been fired and re-fired. The multilayer chip inductor is made by the above processes.
Since this type of the multilayer ceramic electronic components including the above multilayer chip inductor need a process for forming the through hole to the green sheet for connecting the conductor pattern through the green sheet in the manufacturing process. The through hole forming process is executed in such a manner that the green sheet is inserted between a vertically movable upper mold having a punch and a lower mold having a die hole corresponding to the punch and a hole is punched to the green sheet by raising and lowering the upper mold while moving the green sheet, or the upper mold and the lower mold.
However, the above through hole forming method has a problem that since the mechanical vibration and impact resulting from the vertical movement of the upper mold is liable to be transmitted to the green sheet and further the upper mold and the lower mold come into contact with the green sheet in processing, by which the fragile green sheet is dislocated and deformed and the accuracy of shape and the positional accuracy of the through hole is adversely affected.
Since the green sheet used to manufacture the ceramic multilayer electronic components is very weak in strength because its thickness is only about tens of microns, it is liable to be subjected to deformation such as a wrinkle, a broken shape and the like while it is transported between respective processes, which causes a problem that the electrical properties of components are dispersed and trouble is additionally required to remove a deformed green sheet.
Since the conductor pattern is formed by directly printing the fluid conductor paste to the green sheet, there is a problem that when the ceramic green sheet has pinholes, cracks and the like, the conductor paste invades into the portions and causes failures such as the change of inductance, short-circuit and the like. In addition, there is also a problem that when the solvent contained in the conductor paste is not suitable with the green sheet, the solvent penetrates into the ceramic green sheet and makes a sheet attack (tear) or makes deformation such as a shrinkage or a wrinkle in firing, so that the positional accuracy of the conductor pattern and the relative accuracy between the conductor pattern and the through hole are greatly lowered.
Further, since the punching process using the upper mold and the lower mold fundamentally forms a penetrated, when the process is applied to the green sheet formed on the base film, through hole is also formed to the base film as well as the green sheet. Therefore, when the conductor pattern is formed to the green sheet, the conductor paste is filled up to the through hole of the base film in printing. Thus, there arise problems that when the green sheet is peeled from the base film, since the conductor paste filled in the through hole is almost left to the base film side, the fragile green sheet is broken, the amount of the paste in the through hole is reduced and the conductor pattern cannot be satisfactorily connected.